The present invention relates generally to gas turbine engine combustors, and more particularly, in one form, to a gas turbine engine premixing module including a pilot premixing module surrounded by a main premixing module.
Air pollution emissions are an undesirable by-product from the operation of a gas turbine engine that burns fossil fuels. The primary air polluting emissions produced by the burning of fossil fuels include carbon dioxide, water vapor, oxides of nitrogen, carbon monoxide, unburned hydrocarbons, oxides of sulfur and particulate. Of the above emissions, carbon dioxide and water vapor are generally not considered objectionable. However, air pollution has become a worldwide concern and many nations have enacted stricter laws regarding the discharge of pollutants into the environment.
Gas turbine engine designers have generally accepted that many of the by-products of the combustion of a fossil fuel can be controlled by design parameters, the cleanup of exhaust gases and regulating the quality of fuel. Oxides of Nitrogen (NOx) are one of the pollutants that have been of particular concern to gas turbine engine designers. It is well known that in a gas turbine engine the oxidation of nitrogen is dependent upon the flame temperature within the combustion region. Many gas turbine engines utilize some premixing of the main fuel with the compressor air to create a reactant mixture with lean stoichiometries to limit flame temperature and control NOx formation. Typically, a premixing section within the combustor prepares a combustible main fuel mixture upstream of the flame front, and therefore the combustor includes provisions to keep the flame from entering or igniting within the premixing section. Often the residence time and velocities within the premixing section are manipulated to discourage auto-ignition and flashback. As a result of this manipulation the residence time is many times limited, which results in incomplete mixing with increased NOx emission. Further, in many systems the burning temperatures are low enough that Carbon Monoxide (CO) emissions are increased.
Heretofore, there has been a need for an improved apparatus for forming a combustion mixture within a gas turbine engine. The present invention satisfies this and other needs in a novel and unobvious way.